Create composite index from a Django model

Question

I have the following model:

from django.db import models

class PopulationData(models.Model):
    slot = models.IntegerField(db_index=True)
    sample = models.IntegerField()
    value = models.FloatField()

    class Meta:
        unique_together = (('slot', 'sample'),)

And I would like to create also a compound index on the column pair that have the UNIQUE constraint, like so:

CREATE INDEX my_compound_index ON myapp_populationdata (slot, sample);

Right now I have a separate code connected to the post_syncdb signal that issues the previous SQL statement. Is there any way to indicate it from the model specification? (Note: I’m using the 1.3 branch).

Asked By: C2H5OH

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Source

Answer 1

I think that’s not currently implemented in the django ORM.

If you use a migration tool (like south) that might be a good place to add that sql statement or if you preffer to avoid raw sql you could use sqlalchemy (core) but this case sounds simple enough to just go with sql.

Answered By: gonz

Answer 2

Starting from django-1.5 you can make compound index using index_together meta option:
https://docs.djangoproject.com/en/dev/ref/models/options/#index-together

Note index_together is deprecated since django-4.2. Instead, use much more powerful indexes meta option. With it you can create not only compound indexes, but also other types of indexes, e.g. function-based indexes, partial (conditional) indexes, covering indexes:
https://docs.djangoproject.com/en/dev/ref/models/options/#django.db.models.Options.indexes

Answered By: Eugene Prikazchikov

Answer 3

Starting from Django-1.11 use Meta.indexes option https://docs.djangoproject.com/en/1.11/ref/models/indexes/:

from django.db import models

class PopulationData(models.Model):
    slot = models.IntegerField(db_index=True)
    sample = models.IntegerField()
    value = models.FloatField()

    class Meta:
        unique_together = (('slot', 'sample'),)
        indexes = [
            models.Index(fields=['slot', 'sample']),
        ]

Answered By: Artem Likhvar

Answer 4

Since a unique constraint also creates an index, it would be counterproductive to create both.

for example, from the postgres docs:

There’s no need to manually create indexes on unique columns; doing so would just duplicate the automatically-created index.

Credit to Mark Byers for the doc link

If for some reason you still want to create a multi-column index, you can do so via index_together:

class PopulationData(models.Model):
    ...

    class Meta:
        index_together = [['slot', 'sample']]

Answered By: Lord Elrond

Answer 5

Note: index_together may be deprecated in the future:
https://docs.djangoproject.com/en/dev/ref/models/options/#index-together

Use indexes in the Meta class instead:

from django.db import models

class Customer(models.Model):
    first_name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)

    class Meta:
        indexes = [
            models.Index(fields=['last_name', 'first_name']),
            models.Index(fields=['first_name'], name='first_name_idx'),
        ]

Answered By: Boketto

Create composite index from a Django model

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